cell c stop robbing customer

I have a cellphone contract with cell which was due to end at the end of April 2018 ( 24 months) , I made a call to the cell c call Centre in second week of April to cancel the contract and advised them I no longer need their service and there should stop and cancel all debits order to my account, the agent said the she will cancel the contract and because I was suppose to call a month earlier to cancel , there will also debit for the end of may, I even sent mails to their call Centre with my ID number and cell no but it the end of June , cell c is still debiting my account whilst I don't even use their sim card.